This invention relates to a boat hull which comprises a relatively stiff but flexible sheet, preferably in the preform of a flat piece of material or blank, which forms the body or shell and the bottom and which is provided with at least two first edges which are disposed substantially at a right angle to the boat hull center-line and which each extend from one outer edge of the sheet towards the center-line, said sheet being slotted in the direction of or parallel to the center-line or, alternatively, divided into two sheets in the direction of said center-line, said sheet or sheets after being bent or folded along the center-line and parallel thereto being joined together along the slot edges and, where applicable, also joined to an inserted square stern.
The invention also relates to a stiff, but flexible, and preferably flat material or blank in sheet form for utilization in the production of a boat hull as specified hereinbefore, such material or blank comprising two first edges, which are disposed substantially at right angles to a center-line of the blank and which each extend from one respective outer edge of the sheet and towards the said center-line, said sheet being provided with one or more slots extending substantially in the direction of or parallel to the center-line, or such sheet alternatively being divided into two sheets along said center-line.
The invention also relates to a method of producing a boat hull as specified hereinbefore, such method comprising providing a relatively stiff, but flexible, sheet of material or blank formed preferably as a flat piece of material or blank, with at least two first edges disposed substantially at right angles to a center-line of the blank, so that each of said first edges extends from one respective outer edge of the sheet and towards said center-line, and with one or more slots which extend substantially in the direction of or parallel to the center-line or, alternatively, said sheet is divided into two sheets along said center-line.
It is already known to form slots in a flat blank having a triangular cut-out, and to join the edges of the cut-out in order to form the flat sheet or blank into the final desired shape. Applications of this technique are found, for example, in the production of collapsible or folding boats.
Developments in the production of small boats of the fishing or leisure type during recent decades have been marked by a production technique based on reinforced plastic materials. New stricter enviromental regulations applicable to workplaces and the related inferior resistance due to new plastics used in the manufactured hull necessitate other production methods. One of the most interesting alternatives should be the production technique based on flat blanks or sheets as the starting material. The following alternative building materials may be applicable: steel sheets made from various alloys; aluminium from various alloys; plywood, consisting of various types of wood and constructed with different glueing techniques, such plywood blanks being produced in flat plate presses; and plastic blanks of homogeneous material or panels molded together and comprising an external finish section and a structural section. Common to all these materials is that because they are made in relatively small sizes, they generally have to be joined together to form a larger unit covering the entire sides of the hull. Where the term "body blank" is used hereinafter, this expression applies both to blanks which are joined together to form a larger blank before the actual body forming work, and factory-produced blanks of the required size.
A common factor in the known applications is that a point of varying conspicuousness occurs in the finished surface at the tip ends of the slots as a result of folding or bending, and this point readily occurs in the form of a projection, even after grinding down or working thereon in some other way. Such slots are usually made in the bow of the boat hull in order to form the stem shape. Typical slots of this kind are shown in U.S. Pat. No. 2,634,436. The boat shape shown therein, however, presupposes a certain double curvature of the flat starting material. Similar boat shapes are shown in U.S. Pat. No. 2,778,035, where the double curvature requirement is further stressed, and in U.S. Pat. No. 2,515,162.
Although only folds are shown instead of slots, U.S. Pat. No. 2,969,551 is relevant in this context. This patent shows a foldable boat of flat starting material. The known method illustrated, however, has no practical value, firstly because of the resulting boat shape and secondly because of difficulties in finding foldable material with adequate strength in the flat or singlebend surfaces.
The oldest method of producing boat hulls from flat starting material is based on structural steel techniques. Recent alloys have brought light metal constructions to the fore, but, in particular, the modern glueing techniques should promote hull constructions of plywood in every case in lighter-weight boats. A considerable quantity of boats of this type has been built and although developments have been relatively slow because of competition from reinforced plastic as a building material, there is already a highly developed tradition. The common factor in all constructions made from these materials, however, is the sharp bilges forming where the bottom and side walls are joined. An attempt has been made to reduce these bilges by the insertion of stringers, of round shape, to give part of the side walls a partly horizontal and a partly vertical curvature. Despite these steps, the boat hull is considered to be "boxy", a condition which, particularly in the case of motor boats, is accepted as hydrodynamically correct for hulls of the planing type. In this case the shapes are also camouflaged by web plates which are necessary for correct operation of the hull.
Particularly in the production of sailing boats, other parts of the fittings have been utilized as structural elements in cases where the hull is made from plywood. This process is described, inter alia, by Per Brohall in his book "Bygg baten sjalv". This method saves both labor and material but it has had less applicability to metal hulls because the joining together of the metal plates by welding may result in damage to the fittings or may require extensive protective precautions.
The common feature of the prior art is that the hulls produced were given an exactly predeterined shape from the start by fitting the shell or body directly on a frame structure or on the internal fittings fixed bulkheads, beams, spacers at the stowage compartments or the like. Only in exceptional cases have fishing boat hulls been produced by forming the clinker shell against external sub-frames and then providing them with a frame shaped according to the resulting shell.
The object of the present invention is to use as a starting material a complete flat body blank which covers the entire port and starboard sides including the bottom, or alternatively a blank covering the entire body requirements, to allow a boat hull to be formed without sharp bilges or kinks into substantially any desired body shape.